Medication infusion pumps that supply a medication to a patient at a substantially constant flowrate are known. Exemplary infusion pumps are described in U.S. Pat. No. 3,731,681, to Blackshear; U.S. Pat. No. 3,951,147, to Tucker et al.; U.S. Pat. No. 5,167,633, to Mann et al.; and U.S. Pat. No. 5,722,957, to Steinbach. Modern infusion pumps have been developed that are implantable into the body of a patient, particularly a human patient, to whom the medication is to be supplied.
Known infusion pumps typically include a housing that contains a medication chamber and a propellant chamber, together with appropriate means for loading the selected medication into the medication chamber and for supplying the medication to the patient. The propellant chamber typically contains a gaseous or liquid/vapor propellant at a pressure above atmospheric pressure, and applies a predetermined positive pressure to the medication within the medication chamber. This affords a substantially continuous and constant flow of the medication to the patient.
Modern environmental concerns mandate that propellants employed in the foregoing infusion pumps, as well as other devices requiring propellants, be environmentally benign. It is of particular concern to avoid propellants that have an adverse effect on ozone.
A need exists for a medication infusion pump that employs an improved propellant. It would be particularly desirable to provide a medication infusion pump that employs a propellant that is not ozone-depleting.